Farmers markets (agromercados or mercados agropecuarios) exist throughout Havana [1]. State-run hard-currency groceries charge exorbitantly for packaged goods, but you have no other option.
The agromercado is on Avenida de la Bélgica (Egido) (e/ Apodada y Corrales).
Imported meats are sold at La Monserrate (Monserrate, e/ Brasil y Muralles), an air-conditioned butcher shop, and at Harris Brothers (Monserrate #305, e/ O’Reilly y Progreso, Habana Vieja, tel. 07/861-1644, daily 9 a.m.–6 p.m.), a department store with various foodstuff sections.
Supermercado Isla de Cuba (Máximo Gómez #213, esq. Factoria, tel. 07/33-8793, Mon.–Sat. 10 a.m.–6 p.m., Sun. 9 a.m.–1 p.m.), on the south side of Parque de la Fraternidad [2], is reasonably well stocked.
Havana’s largest agromercado is Cuatro Caminos [3] (Máximo Gómez, esq. Manglar, tel. 07/870-5934, Tues.–Sat. 7 a.m.–6:30 p.m., Sun. 7 a.m.–2 p.m.).
Almacenes Ultra (Av. Simón Bolívar #109, esq. Rayo, Mon.–Sat. 9 a.m.–6 p.m., Sun. 9 a.m.–1 p.m.) is a reasonably well-stocked grocery. Similarly, try the basement supermarket in La Época (Galiano, esq. Neptuno, Mon.–Sat. 9:30 a.m.–9:30 p.m., Sun. 9 a.m.–1 p.m.).
There are agromercados at Calle 15 (esq. 10), Calle 17 (e/ K y L), Calle 19 (e/ F y Av. de los Presidentes), Calle 21 (esq. J), (Calle 16 e/ 11 y 13), and Pozos Dulces (e/ Av. Salvador Allende and Bruzón).
There’s a grocery stocking Western goods, plus a bakery, on Calle 17 (e/ M y N, Mon.–Sat. 9 a.m.–6 p.m., Sun. 9 a.m.–1 p.m.).
Also try Supermercado Meridiano (1ra, esq. Paseo, in the Galería del Paseo, Mon.–Sat. 10 a.m.–5 p.m., Sun. 10 a.m.–2 p.m.).
Supermercado 70 (3ra Av., e/ 62 y 70, Miramar, tel. 07/204-2890, Mon.–Sat. 9 a.m.–6 p.m., Sun. 9 a.m.–1 p.m.) is Cuba’s largest supermarket selling imported foodstuffs.
The next best-stocked grocery is Diplo Mercado Miramar (Mon.–Sat. 10 a.m.–6 p.m., Sun. 9 a.m.–1 p.m.), in the Havana Trade Center.
You can buy delicious pastries and breads at Doña Neli Panadería Dulcería (5ta Av., esq. 42, Mon.–Sat. 7 a.m.–6 p.m., Sun. 7 a.m.–1 p.m.), in the Quinta y 42 shopping complex, and at La Francesa del Pan (Calle 42, esq. 19, tel. 07/204-2211).
Links:
[1] http://www.moon.com/destinations/cuba/havana
[2] http://www.moon.com/destinations/cuba/havana/sights-habana-vieja/parque-de-la-fraternidad
[3] http://www.moon.com/destinations/cuba/havana/sights-centro-habana/cerro